Answer
1. Create a file called "athena.properties" with the following text as an example:
jdbc:awsathena://AwsRegion=us-east1;User=USER;Password=SecretAccessKey;S3OutputLocation=s3://aws-athena-query-results-665028136136-us-east-1/;LogLevel=5;LogPath=C:\\temp
2. Replace USER, SecretAccessKey, and the value after S3OutputLocation with the values necessary to connect. The above AwsRegion and S3OutputLocation are provided as an example of proper strings. Region is required at the end.
3. After creating the file, place the file in your "My Tableau Repository\Datasources" (or similar Tableau Prep) folder and then proceed with the standard clean logs gathering process and attempt to establish a new connection with Athena.
This should create a new "jdbcserver.log" file in the "My Tableau Repository\Logs" folder.